in memory database

[Geal]

Right now, the metrics are stored in a very naive way:

pub struct Metrics {
  series: HashMap<String, Serie>,
  counter: usize,
}

pub struct Serie {            
  pub metric_type: MetricType,
  pub values: Vec<Value>,           
}

pub struct Value {                                                                        
  pub timestamp: Timespec,
  pub tags:  Vec<Tag>,
  pub value: isize,
}

pub struct Tag {
  pub key:   String,
  pub value: String,
}

pub enum MetricType {
  Counter,
  Timing,
  Gauge,
}

This is fine for debug sessions and demos, but if the server runs for some time, memory usage gets high.

What can be done here? I remember some people were working on in memory column databases:
https://www.reddit.com/r/rust/comments/93ikxz/emulating_japlkdb_take_2_how_store_columnar_data/
https://crates.io/crates/column

Maybe we can reuse something here?

This should help with #3 and #4 (to do complex queries, we need a database that supports it)